People are being urged to think twice before visiting relatives in hospital if they have the winter vomiting bug known as norovirus.
They are also being asked to stay away if they have cold or flu-like illnesses, in a bid to stop the bugs spreading.
Amanda Howell, lead for infection prevention and control at the Leicestershire Partnership NHS Trust, said: "Norovirus is spread easily and can survive in the environment for many days.
"In hospitals, norovirus increases the risk to patients who might already have other serious illnesses and it can lead to staff illness and even ward closures.
"There is a lot that visitors can do to help us reduce the risk of norovirus and other winter bugs on our wards.
"Thorough, effective hand washing is the single most important way of preventing the spread of infection.
"It is also particularly important that anyone visiting friends and relatives in hospital avoids bringing in home-made food since the risk of infection is particularly high."
Liz Collins, lead nurse for infection prevention at Leicester's hospitals, said: "We always see an increase in these types of illnesses in the winter, but in most cases it can be managed safely and effectively at home.
"To people feeling ill, my advice is to stay at home, keep warm and drink lots of fluids. If they are not feeling better after 48 hours, they should call their GP."
